Reconfigurable Intelligent Surface assisted Two–Way Communications: Performance Analysis and Optimization

Abstract

<jats:p>In this paper, we investigate the two-way communication between two users assisted by a re-configurable intelligent surface (RIS). The scheme that two users communicate simultaneously in the same time slot over Rayleigh fading channels is considered. The channels between the two users and RIS can either be reciprocal or non-reciprocal. For reciprocal channels, we determine the optimal phases at the RIS to maximize the signal-to-interference-plus-noise ratio (SINR). We then derive exact closed-form expressions for the outage probability and spectral efficiency for single-element RIS. By capitalizing the insights obtained from the single-element analysis, we introduce a gamma approximation to model the product of Rayleigh random variables which is useful for the evaluation of the performance metrics in multiple-element RIS. Asymptotic analysis shows that the outage decreases at $\left(\log(\rho)/\rho\right)^L$ rate where $L$ is the number of elements, whereas the spectral efficiency increases at $\log(\rho)$ rate at large average SINR $\rho$. For non-reciprocal channels, the minimum user SINR is targeted to be maximized. For single-element RIS, closed-form solutions are derived whereas for multiple-element RIS the problem turns out to be non-convex. The latter is relaxed to be a semidefinite programming problem, whose optimal solution is achievable and serves as a sub-optimal solution.</jats:p>

Hybrid automatic repeat request‐based intelligent reflecting surface‐assisted communication system

“…As in [3], it is also assumed that the signals reflected only once by the IRS are much more significant than the signals reflected multiple times, which are thus ignored. We also consider the case as in [6–9], where the reflectors of the IRS are separated large enough such that the elements of the vectors h SR and h RD are independent. Further, Rayleigh fading is considered for the links between the IRS and S and between the IRS and D .…”

Two-timescale Beamforming Optimization for Intelligent Reflecting Surface Enhanced Wireless Network

“…Step 1: Generate a mini-batch {H t j } of B channel samples according to the known S-CSI and update the surrogate functionsf t k (θ, λ), ∀k ∈ K, by (21), where {w J k (θ t , λ t ,H t j )} are obtained by employing Algorithm 1 to solve problem (16) with given generated channel samples and fixed (θ t , λ t ).…”

“…• Apply Algorithm 1 to solve problem (16) with given λ and {h k } to obtain {w k } for each time slot.…”

Joint active and passive beamforming optimization for multigroup multicast system aided by intelligent reflecting surface

“…The maximum sum-rate of an IRS-based multiuser MIMO system was studied in [11], but only the downlink was con-sidered. So a two-way communication system was investigated in [12,13], where the IRS and full-duplex were combined to improve the spectrum efficiency and energy efficiency of the system. Comparing with [12], the authors of [13] also took the direct link between BS and users into account, and the system sum rate was maximized by jointly optimizing the source precoders and the IRS phase shift matrix.…”

“…So a two-way communication system was investigated in [12,13], where the IRS and full-duplex were combined to improve the spectrum efficiency and energy efficiency of the system. Comparing with [12], the authors of [13] also took the direct link between BS and users into account, and the system sum rate was maximized by jointly optimizing the source precoders and the IRS phase shift matrix. And the secure IRS assisted two-way communication scheme was proposed in [14].…”